Analyte samples can be delivered to an ionization source of a mass spectrometer in a variety of forms, in solid, liquid and gaseous phases. When analytes are provided in liquid and gaseous phases, they are typically sorted by chromatography, either high performance liquid chromatography (HPLC) for liquid analytes, or gas chromatography (GC) for gas analytes. Separation of analyte molecules allows the mass spectrometer downstream to evaluate the analyte molecules sequentially so that they can be more easily scanned in a mass analyzer.
Chromatography requires specialized instrumentation, such as separation columns, and an appropriate interface to an ionization source. Moreover, the chromatography separation process often takes an hour or more to complete. The instrumentation may not be available outside of the laboratory context and the duration of the separation process may be an inconvenience when it is desired to identify a trace substance quickly. As an example, at a location where it is believed that a small, but possibly dangerous level of a toxic substance has been released into the atmosphere, it would be desirable to analyze a sample of ambient air at the location for the toxic substance directly, without necessarily having to pass the sample through a chromatography apparatus.